TOM'S ARM. Tom's crippled arm leaves him a weaker man physically (not unlike the tiny mockingbird), and it serves as the proof that he was incapable (i.e. innocent) of committing the act of which he was accused.
TOM'S GOODNESS. A humble family man with a wife and children, Tom's biggest mistake was setting foot in the Ewell house in the first place. His intent was only to help Mayella and provide some needed assistance (i.e. happiness) in a household that provided Mayella little comfort or support.
PITY FOR MAYELLA. Tom probably regretted admitting that he "felt right sorry" for Mayella, but under normal circumstances, it was a righteous emotion, and his intentions were pure.
TOM'S FLIGHT. Though Tom's attempt to escape does not show an innocent side, it is symbolic of a bird trying to fly freely from within a caged area. In doing so, Tom decided to climb the fence to freedom rather than attempt to forcibly overpower the guards.
I'll get you started: 1. Tom Robinson never hurt anyone. 2. Tom Robinson never had a chance against bigger, stronger adversaries. 3. Tom Robinson was trying to do something nice (sing a pretty song).